Process of oxidizing mercury



H. W. MATHESO N.

PROCESS OF OXIDIZING MERCURY.

APPLiCMlON FILED DEC, 4. 1917.

1,3? 9,4650 Patented May 24, 11921.

/77 l/enfor" Howard W/Vaf/mson ing application,

UNITED STATES Parent ferries.

'JTEUUESS 0'5 OXIDIZIITG MERCURY.

Specification of Letters Patent.

Patented May 234, 19231.

Application filed December 1, 1917. Serial No. 205,378.

To all whom it may concern:

Be'it known that I, HOWARD W. MATE- SON, a subject of the King of Great Britain, and resident of Shawenegan Falls, in the Province of Quebec and Dominion of Canada, have invented certain new and useful Improvements in Processes of Oxidizing Mercury, of which the following'is a full, clear, and exact description.

This invention relates to improvements in process of oxidizing mercury, and the ob-' ject of the invention is to provide a simple, safe and inexpensive process for producing mercuric oxid in a very pure state.

In my copending application, Ser. No. 204:,008, which deals with the manufacture of acetaldehyde using mercuric oxid as a catalyst, it is stated that the sludge or waste product of the process is treated to reclaim the mercury of the catalyst, and the re claimed mercury then oxidized for re-use, so that in efiect, practically none of the catalyst is lost, but simply goes through a process of'decomposition into its original elements and recombination of the reclaimed mercury with a fresh supply of oxygen to re-form the catalyst. In my copend- Serial Number 205,37 9, the method of recovering the mercury from the kettle sludge is dealt with. In this application, the process of combining the mercury with oxygen to form mercuric oxid is described. It will of course be understood that the process is not limited to the manufacture of mercuric oxid solely for use in the manufacture of acetaldehyde, as the oxid may be used for any other purpose desired.

It has been found b experiment that the oxidization can best he carried out electrolytically. According to the present invention, the mercury is oxidized by the passage of an electric current through a suitable alkaline or acid electrolyte, the oxygen being furnished from the decomposition of the electrolyte, and the mercury itself serving as the anode. The current preferred is that of a low volta e and high amperage, this being found to e most suitable by ex periment. @xid, when formed on the surface of the mercury, is removed by agitation of the electrolyte pension in the electrolyte.

In greater detail, the process is as follows :Mercury is placed to a depth of from half an inch to an inch in a suitable pan,

and drawn on in suscell or receptacle, the mercury being insulated from the ground either by providing the receptacle with an insulating lining or by insulating the receptacle itself from the ground. A cathode of iron, nickel or other metal is provided above the mercury anode, electrically separate from the receptacle, and out of contact with the mercury. This cathode is apertured to permit the escape of gas. The receptacle is then charged with a 3% to 10% solution of caustic soda, which acts as an electrolyte, and is of course in contact with both the anode and the cathode. A. stirring device for the electrolyte is provided above the mercury, and is capable of rotating at any desired speed, the rotating means being preferably such that the stirrer may be moved slowly at the commencement of the process and more rapidly at the end, when the electrolyte is heavy with the oxid formed. One side of an electric circuit is connected to the mercury and the other to the cathode, and a current passed through havin an amperage suficient to give about fifty-five amperes per square foot of anode surface exposed to the electrolyte, at a potential difierence of eight to ten volts. The current specified is that preferred for a single cell, but if a number of cells are connected in series, the voltage on the terminals of the series'will obviously be higher in proportion to the number of cells. It

has been found advisable not to use series requiring more than 200 volts, as with larger series and consequently higher voltage, the danger to the operators and the diiiiculty of insulation is increased.

()xygen is liberated on the surface of the mercury and oxidizes it to mercuric oxid. Hydrogen is liberated at the cathode and escapes through the openings in the same. The stirrer is allowed to rotate slowly. As the oxidization proceeds, mercuric oxid forms on the surface of the mercury and the stirrer rotating close to the sui\face serves to keep the mercury surface clean and allow the oxidization to continue. At the end of a half hour, a considerable amount of oxid has accumulated in the cell. The speed of the stirrer is now changed to thoroughly mix this with the electrolyte, and the mercuric oxid in suspension in the electrolyte is drawn ofi near the base of the cell. Fresh electrolyte is, then supplied, the speed of the stirrers decreased and the reaction is continued. This procedure is continued inreturned to the cell.

' cury is recharged periodically electrolyte is drawn off :from

It is necessary to provide means for drawng off the gases formed as the oxldizatlon progresses.

The mercuric mud in suspenslon 1n the as indicated above, and is run to odically 'Mercuric oxid is setsuitable settling vats. tled out in these vats by allowing the solution to stand for a few hours. The clear supernatant electrolyte is then drawn off to suitable storage vats and pumped back to the cells to be used over again.

A considerable amount of heat is given off I by the passage of the current in the process outlined, and the electrolyte is drawn from the cells quite hot. After sedimentation. of the oxid, this electrolyte is cooled, by passing through a water condenser, before it is sent to the storage vats.

Mercuric oxid in the yellow modification is obtained by this process, and, as obtained in the settling tanks, it is mixed with a small amount of electrolyte solution. This oxid is washed once with water and then finally with dilute acid solution. It is then in a suitable state to be used in the manufacture of acetaldehyde, according tomy copending application, Serial No. 204,008.

If the mercuric oxid is to be used for any purpose other than the manufacture of acetaldehyde, it may be obtained in a very pure form by removal of the moisture.

The oxidization of the mercury may, according to the above described process, be carried out in a continuous manner. The cells do not need to be operated until the mercury therein is all oxidized, but the merto keep it at the same level in the bottom of the cell. When carrying on the process continuously,

.as outlined above, a cell having approximately thirty square feet of mercury ex posed will yield between eight and twelve pounds of mercuric oxid per hour.

In a preceding paragraph, it has been statedthat the cell is provlded with a stirring device and a cathode. These may be separate elements, or a single moving element may be used serving both purposes, or-

the cathode may be mechanically but not necessarily electrically connected to the stirrer.

One form of apparatus suitable for carrying out the process is illustrated in section in the accompanying drawing. This. apparatus comprises a pan or suitable vessel 11 having a lining 12 of concrete or other insulating material. A metal anode 13 is the cell eri-- bedded in the lining 12 and is electrically separated from the vessel 11. A layer of mercury 1 1 is provided in the bottom of the pan in contact with the anode and electrically speaking, forms a A cathode 15 is provided above the anode and is preferably in the form of spaced plates which will allow gas generated during the re-action to escape between them. A stirring device 16 is provided in the cell in position to just clear the surface of the mer cury. This stirring device is provided with mechanism 17 for driving it at two-speeds. As shown in the drawings the stirring device 16 is mechanically and electrically separated from the cathode but it is clear that this arrangement neednot be adhered to.

At one side of the vessel 11, and insulated therefrom, is a mercury reservoir 18 having a valve controlled connection with the mercury in the cell. A valve controlled drawofi' pipe 19 is provided leading from the cell a short distance above the level of the mercur aving thus described the invention, what is claimed is 1. A process of oxidizing mercury which comprises using metallic mercury as the anode of an electrolytic cellin connection with a cathode formed of a metal of the iron family and a continuously agitated electrolyte, and periodically agitating the elec trolyte with increased violence.

2. A process according to claim 1,-in which the current employed in the cell is approximately fifty-five amperes per square foot of mercury exposed to the'electrolyte at a potential difference of eight to ten volts.

3. A process according to claim 1, in which the electrolyte is agitated with increased violence as it becomes heavy with oxid, to maintain the surface of the mercury clearof oxid for continued electrolysis and to enable the suspended oxid to be drained off from the cell.

4:. A process of manufacturing an oxid of mercury, which comprises disposing mercury to be oxidized in an electrolytic cellv part of /the anode.

electrolyte becomes heavy with formed oxid to clear the surface of the mercury for further oxidation and to enable the oxid to be removed while in suspension in the 'elec trolyte.

In witness whereof, I have hereunto set my hand.

HOWARD W. MATHESON. 

